The present invention relates to a semiconductor device having an insulation material consisting of an amorphous carbon fluoride film and a method of manufacturing the semiconductor device, and particularly to a semiconductor device having an interlayer insulation film consisting of an amorphous carbon fluoride film in a multilayer wiring structure and a method of manufacturing the semiconductor device.
As the result of the increased integration of large-scale integrated circuit (LSI) composed of semiconductors, individual elements with very small size of 0.25 .mu.m or under are being integrated around the surface of a silicon substrate. An LSI works on the basis of wiring between individual elements. A wiring detour for avoiding crossing of wiring at a mutual connection between individual elements makes wiring areas in a chip area increase and signals due to increased wiring distance delay. For this reason, to avoid the crossing and piling up points of wiring, the insertion of an insulation film between wires is commonly applied for a multilayer wiring technique.
However, a multilayer wiring technique constructed by putting a thin insulation film therebetween has a problem of increasing a stray capacity between different wiring layers or between a wiring layer and a silicon substrate. The problem causes a signal delay in wiring and a cross talk on transmitting through two adjacent wires a signal containing a high frequency component pilling up in upper and down directions. A method to prevent the signal delay and cross talk is to decrease a stray capacity between wiring layers and to increase a distance between upper and lower wires, in other words, thicken an interlayer insulation film. However, this method deepens a contact hole and a via hole opened for connecting between a silicon substrate and a wiring layer or between the upper and lower wiring layers. Dry-etching technique due to forming of the deepened contact hole and via hole become more difficult to operate. Thus, the thickening of interlayer insulation film is not appropriate. For example, when the diameter of a contact hole should be 0.25 .mu.m or less in such field as a semiconductor integrated circuit technology since manufacturing of 256 megabit DRAM (dynamic random access memory,) it is preferred on the point of dry-etching that the ratio called aspect ratio of the diameter of a contact hole to its maximum depth is 5 or less. Consequently, decreasing the stray capacity is required as well as decreasing the thickness of an interlayer insulation film to approximately 1 .mu.m or less. In addition, there is another problem related to an increase in a stray capacity between wires extended on a same surface due to microscopic size as well as the problem occurring between upper and lower wiring layers. Decrease of a semiconductor integrated circuit to a microscopic size requires decrease in the thickness of wires as well as microscopic distance between wires and soon a distance between two wires will become equal to the thickness of the wire. Decrease in distance between wires gives a serious problem of a stray capacity between wires within a same wiring layer. In consideration of higher integration, increasing the distance between wires is impossible and signal delay in the same layer and cross talk are serious problems in contrast with the upper and lower wiring layers, there between an interlayer insulation film can be thickened.
In the present specification, a term of an interlayer insulation film is used for all insulation films including said insulation film between the upper and lower wiring layers, an insulation film between a wiring layer and a silicon substrate, and an insulation film between wires disposed in a same wiring layer.
On these technological backgrounds, a thin insulation film having a small relative dielectric constant .epsilon.r is being developed on the basis that an electrostatic capacity of a same structure proportionally changes to the relative dielectric constant of an insulating material put between electrodes, that signal delay proportionally changes to the square root of the relative dielectric constant of an insulation material, and that using a material of a lower dielectric constant for interlayer insulation film makes decrease in stray capacity between wires and in signal delay possible. For these reasons, replacing such insulation film as Si3N4 (relative dielectric constant .epsilon.r is 7) or SiO2 (relative dielectric constant .epsilon.r is 3.9) well used for LSI technology, a material having a low relative dielectric of 3 or smaller constant allows to solve such problems as signal delay and cross talk avoiding problems such as difficulty to process an interlayer insulation film due to thickening.
For usages of materials with a low relative dielectric constant, a whole body of an interlayer insulation film is consisted of a low relative dielectric constant, or a low relative dielectric constant is used for a part of an interlayer insulation film. For example, making the interlayer insulation film is consisted of double layers its lower layer is consisted of a film of a material of a low relative dielectric constant and upper layer is consisted of conventionally used insulation material such as SiO2. This method provides advantages such as that the problems of stray capacity and cross talk are solved by using a material having a low relative dielectric constant for a central part of serious problems of an interlayer capacity between wires distributed in a same layer and that using such material excellent for processing as SiO2 for the upper layer makes flattening possible. The insulation film of the upper layer explained above is called flattened insulation film hereafter. The capacity between the upper and lower layers in such layered structure is the sum of the serial connection of capacities of the insulation film having a low dielectric constant and the capacity of flattened insulation film. It is possible to adjust an effective relative dielectric constant of a whole interlayer insulation film to a value desired.
An amorphous carbon fluoride film (a-C: F) is disclosed as a material with a low dielectric constant used for the aforesaid purpose in Japanese Unexamined Patent Publications such as 1996-83842, 1996-222557, and 1996-236517. The amorphous carbon fluoride film is recognized as excellent material with a low dielectric constant to solve the problems on the basis that a relative dielectric constant can be reduced approximately 2 according to manufacturing method thereof and fluorine content and that the material shows such good matching with LSI processing as yielding heat-resistant temperature of 400.degree. C. or higher.
As stated before, although the amorphous carbon fluoride film has a low dielectric constant .epsilon.r and is evaluated as a material for interlayer insulation film, commercialization of the amorphous carbon fluoride film has not been realized. The reason is that the amorphous carbon fluoride film contains chemically active fluorine causing problems in technology of making a contact hole and via hole for use in connection of wiring metals, upper and lower layers. The problem is that on contacting an amorphous carbon fluoride film and a wiring metal, the reaction of fluorine contained in the amorphous carbon fluoride film and the metal is inevitably caused to occur in following heat processing step.
The reaction of fluorine contained in the amorphous carbon fluoride film to a metal caused problems stated below. Primarily, the relative dielectric constant of a film increases in accordance with a decrease in fluorine content ratio in the amorphous carbon fluoride film and as a result, a capacity between wires increases. In addition, a metal fluoride generated by the reaction to fluorine shows a higher resistance rather than that of a metal to increase in the resistance of wires. The increase in a capacity between wires and a resistance of a wire causes increase in signal delay. The reaction still causes another problem that the metal fluoride generated by the reaction to fluorine due to relatively low boiling point vaporizes in heat processing step to generate gas. For example, TiF4 generated in the heat processing under a temperature around 300.degree. C. easily vaporizes, because TiF4 generated by the reaction of Ti to fluorine has the boiling point of 284.degree. C. As a result, Ti is lost in the area, where fluorine dispersed, to increase in resistance of wires and resulted in the disturbance of circuit operation, generated bubbles cause swelling or falling portions in the structure formed on the adjacent areas or the upper part of those bubbles, and defects of semiconductor devices.
These problems are not restricted to the case of Ti that is a metal contacting to an amorphous carbon fluoride. The reaction to fluoride is also a problem when W, Al, copper (Cu), or an alloy containing these metals is used for a wire. In addition to said simple structure, the reaction occurs in any semiconductor device having a structure to allow the contact of a metal to an amorphous carbon fluoride. This means that said problem always causes a defect of a semiconductor device from heat processing against contacting parts of any metal with an amorphous carbon fluoride in any contact place and any structure of the semiconductor device. When heat processing is never carried out, after an amorphous carbon fluoride film was formed, a very difficult restriction occurs in the processing. Thus, a structure for preventing the aforesaid reaction is desired.
As a proposal for preventing a reaction of a metal with fluorine, a structure having a buffer layer of an insulation film, such as silicon oxide film or silicon nitride film inserted in the interface between a metal and an amorphous carbon fluoride film is disclosed in Japanese Unexamined Patent Publication 1996-264648. However, it is difficult for the structure made from such insulation film to protect a metal applied to the protection of the side wall of a contact hole or a via hole, because disposition of an insulation film in the inside wall of a hole decreases the sectional area of a buried wiring metal to raise resistance value thereof. Besides, when an insulation film is formed to protect the side wall of a hole, removal of an insulation film on the lower surface of a hole is required to connect upper and lower wiring layers. This requirement causes very difficult processing.